BIOCHEMICAL ACTIVITY OF YEASTS 175 



composes sugars like saccharose or maltose, and whether it ferments 

 others as saccharose, maltose, galactose, fructose, dextrose, lactose, 

 raffinose, melibiose, methylglucoside, dextrine, inulin, etc. This dif- 

 ferential action towards the various carbohydrates is important in 

 the determination of the yeasts. Some will decompose dextrose, others 

 will not. The great majority will not decompose lactose. Lactose- 

 fermenting yeasts are not uncommon, however. Beijerinck 1 (1889) 

 found such a yeast in the Kefir grain. One was also found in Edam 

 cheese by the same author. He called the one from the cheese Sac- 

 charomyces tyrocola and the one from the Kefir grains Saccharomyces 

 kefir. Grotenfeld 2 in the same year found a lactose-fermenting yeast 

 in milk. With regard to these yeasts being true saccharomyces there 

 seems to have been some difference of opinion, since others have been 

 unable to detect the formation of ascospores. Bochicchio 3 isolated a 

 non-spore bearing yeast from Grana cheese which he named Lacto- 

 myces inflans-caseigrana. Freudenreich and Jensen 4 report a lactose- 

 fermenting yeast from Emmenthaler cheese. Jensen 6 later found two 

 such yeasts in butter. Maze 6 when studying ten Torulae from cheese 

 found only one which fermented lactose. The others fermented many 

 of the common carbohydrates. Duclaux reported three lactose ferment- 

 ers. Hunter 7 isolated such a yeast from " foamy " cream and regarded 

 it as the essential organism for this abnormality. The thermal death 

 point of the yeast seemed to be near 55 C. Typical spores were not 

 demonstrated which would seem to exclude it from classification with 

 the Saccharomycetes. Trehalose is rarely fermented by the yeasts. 

 Hansen has been able to subdivide the Saccharomyces into six groups 

 according to their action on the carbohydrates. He has used such 

 characteristics as the production of acetone and other compounds. 



Industrial yeasts are often classified as bottom or top yeasts. 

 In the beer industry, the top fermentation and the bottom fermenta- 

 tion are brought about by certain variations in the method of manu- 



1 Beijerinck, M. W. Die Lactase ein neues Enzyme. Cent. Bakt. Abt. I., 

 6, 44, 1889. 



2 Grotenfeld, G. Studien iiber die Zersetzung der Milch. Cent. Bakt. Abt. 

 I, 5, 607, 1889. 



3 Bochicchio, N. Ueber einen Milchzucker Vergarenden und Kaseblahungen 

 hervorrufenden neuen Hefepilz. Cent. Bakt. Abt. I, 15, 546. 



4 Freudenreich, E. V., and Jensen, O. Ueber die Einfluss des Naturlabes 

 auf die Reifung des Emmenthalerkases. Cent. Bakt. Abt. II, 3, 544. 



6 Jensen, 0. Studien iiber Ranzigwerden der Butter. Cent. Bakt. Abt. II, 

 8, 251. 



6 Maze, P. Quelques nouvelles races de levures de lactose. Ann. Past. Inst. 

 17, II. 



7 Hunter, O. W. A lactose-fermenting yeast producing foamy cream. Jour. 

 Bact. 3, 293-300, 1918. 



